The invention generally relates to mechanical couplings and, more particularly, relates to mechanical couplings for use with power tools and torque calibration equipment.
Efficient transmission of torque loads between two members has been problematic in the hand and power tool industry for many years. Splines, ball detents, keyways, and set screws have been used in various arrangements to couple two components together with external and internal drive elements. These connections add cost, however, and are all not always the most efficient methods of torque transfer.
The hand and power tool internal and external drive square is perhaps the best known example. Such parts are designed to have a removable connection, to allow quick changing of sockets from the working end of the ratchet and/or square drive. To achieve that end, considerable clearances, both across the corners and the flat sides of the drive square are built into the design. Such clearances have been standardized through national (ASME) and international (ISO) organizations to facilitate interchangeability. Such clearances are so large, however, that a ball spring detent system is often needed to prevent the decoupling of the two elements due to a change in position of the drive elements with respect to gravity. Additionally, the design of the square results in a considerable amount of non-perpendicularity tolerance with respect to the drive element.
Moreover, when torque loads are applied to the drive element, the external square makes contact with the corners of the internal square. This contact area is variable due to clearance tolerances in all three planes of engagement. Therefore, coupling stresses may vary considerably, and the center of the square with respect to the theoretical center line varies as well.
While, such lack of precision transfer is a source of inefficiency in terms of torque transfer, it is also a critical source of error and inefficiency in testing and calibration equipment, tools and torque drives.
In accordance with one aspect of the invention, a coupling for a torque transmission device is provided which comprises a body, at least one retaining ball, a pin cone and a set screw. The body includes first and second ends with at least three sides wherein the three sides define at least three corners. Each corner includes an aperture. A retaining ball is positioned within the body proximate each of the apertures and is adapted to move partially through one of the apertures. The pin cone is slidably disposed within the body and includes first and second cam surfaces wherein the first cam surface is adapted to engage each of the retaining balls. The set screw is threadably mounted in the body, and is adapted to engage the second cam surface of the pin cone.
In accordance with another aspect of the invention, a method of coupling at least two torque transmitting devices is provided which comprises the steps of inserting a first body into a second body, and moving retaining balls from one of the first and second bodies into engagement with the other of the first and second bodies. The retaining balls are proximate corners of both the first and second bodies.
In accordance with another aspect of the invention, a coupling is provided which comprises a first body, a second body, means for connecting the first body to the second body, means for adjusting the torque holding capability of the means for connecting, and means for maintaining concentricity between the first and second bodies.
These and other aspects and features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.